Well, I just installed the BFD today and now I'm getting quite a bit of hum from my subs. My setup is as follows. Nad T752 to BFD (DSP 1124) to either a plate amp or a stereo amp. When the subs are calibrated to a 'proper' volume (around the same dB as the mains) I can hear both the subs from listening position. (The T752 has dual sub outs, so I'm using both inputs/outputs on the BFD) I'm using 1/4" TRS connectors on the BFD, but I am using a different brand of cable from the receiver to the BFD and to the amps. (Cheap RCA cables from the receiver to the BFD then coax digital cables from the BFD to the amps.) If I increase or decrese the sub output on the receiver, it doesn't effect the hum at all. If I apply a filter at 63 Hz on the BFD and increase the gain, it does effect the volume of the hum. Also if I increase the volume on either of the amps, it increases the hum. If I go direct from the receiver to either of the amps, the hum is mainly eliminated, your ear needs to be right up against the sub. I am using -4 volt setting on both channels of the BFD. I've plugged the BFD into a different circuit, and it didn't effect the hum any. Any suggestions?